1. Field of the Invention
The present invention relates to a printing apparatus having an eraser for erasing a printed character.
2. Related Background Art
A printing apparatus such as an electronic typewriter is known, which has a correction device for erasing a character printed on a recording medium by painting it white with a correction tape or the like.
A conventional erasure operation for a character or symbol will be described with reference to FIGS. 9 and 10.
FIG. 9 is a flow chart illustrating a conventional print control procedure which includes steps 1 to 16.
Upon turning on the power, the procedure starts by initializing a counter and the like (step 1). After the initializing step, a print mode starts and the apparatus waits for a key input of print information (step 2). Upon a key input (step 3), the key-input information is stored in a print memory (step 4).
Next, it is checked if the oldest key-input data is stored in the print memory (step 5). If NO (step 6), the flow returns to step 5 to await a key-input. If YES, it is checked if the stored data affects the carrier position (step 7). If YES at step 7, the key data is printed (step 8) and the printed data is stored in an output memory (step 9).
Next, it is checked if the printed data is a character or symbol (step 10). If NO, the flow advances to step 13. If YES, it is checked if the printed data is for a superimposing character (step 11). If YES, the flow advances to step 13. If NO, the carrier is moved by one space in the print direction (step 12). The value of a position counter is increased or decreased by the amount corresponding to a displacement of the carrier (step 13).
Next, the oldest data stored in the print memory is erased, i.e., the printed character data is erased (step 14), and the flow returns to step 5.
If NO at step 7, it is checked if the key data is for an erasure key (step 15). If YES, the erasure mode processing shown in FIG. 11 starts. If NO, it is checked if key data is for a code key (step 16). If YES, the code mode processing is executed. If NO, the key-input instruction is executed and thereafter the flow advances to step 13.
FIG. 10 is a flow chart illustrating an example of the processing procedure in the erasure mode according to a conventional printing apparatus, the flow including steps 1 to 4.
It is checked if a character or symbol is stored in the output memory at the carrier position (step 1). If YES, a character or symbol at the carrier position is erased (step 2) and the flow returns to step 14 shown in FIG. 9. If NO, the carrier is moved backward to the position corresponding to the position nearest to a character or symbol stored in the output memory immediately before the present carrier position (step 3). The value of the position counter is decreased by the amount corresponding to a displacement of the carrier (step 4) and the flow returns to step 2.
FIG. 11 is a flow chart illustrating an example of the processing procedure in the manual erasure mode of a conventional printing apparatus, the flow including steps 1 to 18.
A key input is awaited (step 1). Upon a key input (step 2), the key-input information is stored in the print memory (step 3).
Next, it is checked if the oldest key-input data is stored in the print memory (step 4). If NO (step 5), the flow returns to step 4 to wait for a key-input. If YES, it is checked if the stored data is for a relocation key (step 6). If NO, it is checked if the stored data is for an erasure key (step 7). If YES at step 7, the oldest data stored in the print memory is erased (step 8). Thereafter, the oldest data stored in the print memory is checked (step 9). This data may be an erasure code or a character code.
Next, it is checked if the oldest key data is stored in the print memory (step 9). If NO (step 10), the flow returns to step 9. If YES, it is checked if the key information (key code) is for a character or symbol (step 11). If NO, the flow advances to step 13. If YES, the character or symbol is erased (step 12).
Next, the oldest data stored in the print memory is erased (step 13), and the flow returns to step 4.
If YES at step 6, a relocation code is outputted (step 14) to release the manual erasure mode, and the flow returns to step 13 shown in FIG. 9.
If NO at step 7, it is checked if the key data is for a back trace key (step 15). If NO, a key code process for the key data is executed (step 16). The value of the position counter is increased or decreased by the amount corresponding to a displacement of the carrier, and thereafter the flow returns to step 13.
If YES at step 15, a buzzer alarm is effected (step 18) and the flow returns to step 13.
As described above, according to a conventional printing apparatus, after a specific erasure operation for erasing a character or symbol at a certain position is carried out once in the erasure mode, the control immediately returns to the print mode.
In the manual erase mode, in order to erase a character or symbol, it is necessary to carry out a key-input operation two times, one for entering an erasure key and the other for entering a character or symbol to be erased.
In the automatic erasure operation following the control procedure shown in FIG. 9, immediately after executing a specific erasure operation for a character or symbol, the control immediately returns to the print mode. If the erasure performance of a correction tape deteriorates or if a slight displacement of a print sheet occurs during the erasure operation, the specific erasure operation carried out in a conventional printing apparatus becomes unsatisfactory in properly erasing a printed character or symbol.
Also in the manual erasure operation not storing information for a character or symbol to be erased, it is necessary to carry out a plurality of key input operations in order to erase one character or symbol. In addition, after the specific erasure operation, if the same character or symbol at the same position is required again to be erased, a plurality of key-input operations become necessary. The efficiency of the correction operation is therefore considerably lowered as the number of characters or symbols to be erased increases.